Non-aqueous electrolyte batteries, which use lithium as a negative electrode active material, have been widely used as power sources for memory backup, cameras and the like as primary batteries owing to advantages of high voltage, high energy density, small self-discharge and excellent long term reliability. However, in accordance with the recent remarkable development of portable type electronic instruments, communication instruments and the like, a variety of instruments which require large current outputs for batteries as power sources have been developed. Economic considerations and the realization of compact and lightweight electronic instruments demand a secondary battery having a high energy density capable of repeated charge and discharge. Research and development are actively performed for realizing secondary batteries from the aforementioned non-aqueous electrolyte batteries. However, the energy density, the charge and discharge cycle life and the reliability of such secondary batteries have not been satisfactory.
In the prior art, three types of positive electrode active materials for positive electrodes of the foregoing secondary batteries have been used depending on the nature of charge and discharge reactions. The first type is a type in which only lithium ions (cations) enter into and exit from spaces between layers, lattice positions or gaps between lattices of crystals by intercalation and deintercalation reactions and the like, such as various metal chalcogenides such as TiS.sub.2, MoS.sub.2, NbSe.sub.3 and the like, metal oxides such as MnO.sub.2, MoO.sub.3, V.sub.2 O.sub.5, Li.sub.x CoO.sub.2, Li.sub.x NiO.sub.2, Li.sub.x Mn.sub.2 O.sub.4 and the like. The second type is a type in which principally only anions stably enter and exit by dope and undope reactions, such as conductive polymers such as polyaniline, polypyrrole, polyparaphenylene and the like. The third type is a type in which both lithium cations and anions can enter and exit (intercalation, deintercalation, or dope, undope, and the like), such as graphite intercalation compounds, conductive polymers such as polyacene, and the like.
On the other hand, as the negative electrode active materials for the negative electrodes of such batteries, the electrode electric potential is basest when only metal lithium is used, so that preferably the output voltage and energy density are highest when applied in a battery having a positive electrode using a positive electrode active material as described above. However, there have been such drawbacks in that dendrite and passivation compounds are generated on the negative electrode during charge and discharge, deterioration due to charge and discharge is large, and the cycle life is short. In order to solve such problems, it has been proposed to use a negative electrode active material capable of absorbing and releasing lithium ions such as (1) alloys of lithium and other metals such as Al, Zn, Sn, Pb, Bi, Cd and the like, (2) intercalation compounds or insertion compounds in which lithium ion is incorporated in crystal structures such as inorganic compounds such as WO.sub.2, MoO.sub.2, Fe.sub.2 O.sub.3, TiS.sub.2 and the like, graphite, carbonaceous materials obtained by calcinating organic materials and the like, and (3) conductive polymers such as polyacene, polyacetyline and the like in which lithium ion is doped.
However, generally when a battery is formed by combining a negative electrode having a negative electrode active material capable of absorbing and releasing lithium ions other than metal lithium as described above, and a positive electrode using a positive electrode active material as described above, the negative electrode active material has an electrode electric potential which is nobler than the electrode electric potential of metal lithium, so that there is a drawback in that the working voltage of the battery is fairly lower as compared with a case in which only metal lithium is used as the negative electrode active material. For example, the working voltage is lower by 0.2-0.8 V when an alloy of lithium and Al, Zn, Pb, Sn, Bi, Cd or the like is used, it is lower by 0-1 V in the case of a carbon-lithium intercalation compound, and it is lower by 0.5-1.5 V in the case of a lithium ion insertion compound such as MoO.sub.2, WO.sub.2 and the like.
In addition, elements other than lithium also serve as negative electrode constituting elements, so that the capacity and the energy density per volume and weight are remarkably lowered.
Further, when the alloy of lithium and the other metal in the aforementioned (1) is used, there is such a problem that the utilization efficiency of lithium during charge and discharge is low, and the cycle life is short due to generation of cracks in the electrode by repeated charge and discharge causing breakage of the electrode. In the case of the lithium intercalation compound or the insertion compound of (2), there is a drawback in that there is deterioration such as the collapse of the crystal structure, the generation of irreversible by-product materials and the like by excessive charge and discharge, and there are many ones having high (noble) electrode electric potentials, so that the battery using it has a low output voltage. In the case of the conductive polymer of (3), there is such a problem that the charge and discharge capacity, especially the charge and discharge capacity per volume, is small.
Thus, in order to obtain a secondary battery having a high voltage and a high energy density in which the charge and discharge characteristics are excellent and the cycle life is long, a negative electrode active material is necessary in which the electrode electric potential with respect to lithium is low (base), there is no deterioration such as the collapse of the crystal structure due to absorption and release of lithium ions during charge and discharge and there is no generation of irreversible materials and the like, and an amount capable of reversibly incorporating and releasing lithium ion, that is an effective charge and discharge capacity is larger.
On the other hand, with respect to the aforementioned positive electrode active materials, the first type generally has a large energy density but has such a drawback that deterioration is large due to the collapse of crystals and the generation of irreversible materials and the like due to excessive charge and excessive discharge. In addition, the second and third types reversely have such a drawback that the charge and discharge capacity, especially the charge and discharge capacity and the energy density per volume, are small.
Thus in order to obtain a secondary battery having a high capacity and a high energy density in which the excessive charge and excessive discharge characteristics are excellent, a positive electrode active material is necessary in which there is neither the collapse of crystals nor the generation of irreversible materials due to excessive charge and excessive discharge, and the amount capable of reversibly incorporating and releasing lithium ion is larger.